The present invention relates, in general, to a surgical fastener and, more particularly, to a surgical fastener for attaching a prosthetic in the repair of a defect in tissue such as an inguinal hernia.
An inguinal hernia is a condition where a small loop of bowel or intestine protrudes through a weak place or defect within the lower abdominal muscle wall or groin of a patient. This condition commonly occurs in humans, particularly males. Hernias of this type can be a congenital defect wherein the patient is born with this problem, or can be caused by straining or lifting heavy objects. Heavy lifting is known to create a large amount of stress upon the abdominal wall and can cause a rupture or tearing at a weak point of the abdominal muscle to create the defect or opening. In any case, the patient can be left with an unsightly bulge of intestinal tissue protruding through the defect, pain, reduced lifting abilities, and in some cases, impaction of the bowel, or possibly other complications if the flow of blood is cut off to the protruding tissue.
A common solution to this problem is surgery. In the surgical procedure, the defect is accessed and carefully examined, either through an open incision or endoscopically through an access port such as a trocar. In either case, the careful examination can be well appreciated, as a network of vessels and nerves exist in the area of a typical defect, which requires a surgeon to conduct a hernia repair with great skill and caution. Within this area are found vascular structures such as gastric vessels, the external iliac vessels, and the inferior epigastric vessels, and reproductive vessels such as the vas deferens extending through the inguinal floor.
Once the surgeon is familiar with the anatomy of a patient, the surgeon carefully pushes the bowel back into the patient""s abdomen through the defect. Repairing the defect can involve closure of the defect with sutures or fasteners but generally involves placing a surgical prosthetic such as a mesh patch over the open defect, and attaching the mesh patch to the inguinal floor with conventional suture or with surgical fasteners. The mesh patch acts as a barrier and prevents expulsion of bowel through the defect. Suturing of the mesh patch to the inguinal floor is well suited to open procedures but much more difficult and time consuming with endoscopic procedures. With the adoption of endoscopic surgery, endoscopic surgical instruments that apply surgical fasteners are falling more and more into use. However, the tissue of the inguinal floor offers special challenges to the surgeon when a needle or fastener is used to penetrate structures such as Cooper""s ligament.
At present, there are a variety of surgical instruments and fasteners available for the surgeon to use in an endoscopic or open procedure to attach the mesh patch to the inguinal floor. One of the earliest types of endoscopic surgical instruments used is a surgical stapler. These surgical instruments apply a plurality of elongated xe2x80x9cUxe2x80x9d shaped staples, one at a time, into the mesh patch and the inguinal wall. The xe2x80x9cUxe2x80x9d shaped staples are formed into a box that digs into tissue as it is formed and tightly holds the mesh patch onto tissue. A plurality of these unformed staples are generally contained within a stapling cartridge in a serial fashion, and are sequentially advanced or fed from the instrument with a spring mechanism. Surgical fasteners of these types are found in U.S. Pat. No. 5,470,010 by Robert Rothfuss et al. and in U.S. Pat. No. 5,582,616, also by Robert Rothfuss et al.
Whereas these surgical stapling instruments did indeed adequately fasten the mesh patch to the inguinal wall, their usage has declined due to a surgeon perception that a smaller diameter instrument was needed for endoscopic procedures. Surgeons have begun to use smaller 5 mm devices that offer a smaller access incision in the abdomen than a 10 mm diameter stapler does. Some of these smaller devices use a different type of fastener, such as a helical wire fastener that resembles a small section of spring. Multiple helical wire fasteners are stored serially within the 5 mm shaft, and are corkscrewed or rotated into tissue. A drive bar extends across the proximal end of the helical fastener and holds the mesh patch against tissue. As the instrument is fired, a load spring is used to bias or feed the remaining helical fasteners distally. Instruments and fasteners of these types are found in U.S. Pat. No. 5,582,616 by Lee Bolduc et al., U.S. Pat. No. 5,810,882 by Lee Bolduc et al., and in U.S. Pat. No. 5,830,221 by Jeffrey Stein et al.
Other surgical fasteners and surgical application instruments have been tried, for example dart fasteners that utilizes a single shot plunger type applicator, and xe2x80x9cHxe2x80x9d shaped clothes tie type fastener that also uses a plunger type applicator. The dart fastener has a pointed distal end with retaining barbs, and a large disk at the distal end. The fastener is described as being formed of polypropelene, stainless steel or polydioxanone suture. To apply, the surgeon drives the pointed end into the mesh patch and into tissue. The barbs retain the pointed end within tissue and the large disk retains the mesh patch against the inguinal floor. For multiple fastener firings, a rotary feeding magazine is employed. The xe2x80x9cHxe2x80x9d shaped clothing tag fastener is also described in the prior art. A first vertical leg of the xe2x80x9cHxe2x80x9d mounts within a needle of an applier with the horizontal bar of the xe2x80x9cHxe2x80x9d and the second or remaining vertical leg of the xe2x80x9cHxe2x80x9d sticking out. The needle is plunged into the mesh patch and into tissue, and the first vertical leg is then ejected to lock into tissue, bringing the second vertical leg into contact with the mesh patch. The xe2x80x9cHxe2x80x9d fasteners are also made of polypropelene, stainless steel or polydioxanone suture. Both of these types of fasteners and surgical fastening instruments can be found in U.S. Pat. No. 5,203,864 and U.S. Pat. No. 5,290,297, Both by Edward Phillips. These instruments have not gained acceptance by the surgical community, possibly due to their single shot capabilities and the large size of the rotary magazine.
Whereas the above fasteners are utilized to attach a prosthetic within the body for the repair of a hernia, none of the fasteners disclosed are formed from a superelastic or pseudoelastic shape memory alloys. These alloys exhibit characteristics that can be used to advantage in the fastener. The prior art makes reference to the use of alloys such as Nitinol (Nixe2x80x94Ti alloy) which have shape memory and/or superelastic characteristics in medical devices which are designed to be inserted into a patient""s body. The shape memory characteristics allow the devices to be deformed to facilitate their insertion into a body lumen or cavity and then be heated within the body so that the device returns to its original shape. Superelastic characteristics on the other hand generally allow the metal to be deformed and restrained in the deformed condition to facilitate the insertion of the medical device containing the metal into a patient""s body, with such deformation causing the phase transformation. Once within the body lumen the restraint on the superelastic member can be removed, thereby reducing the stress therein so that the superelastic member can return to its original un-deformed shape by the transformation back to the original phase. Alloys having shape memory/superelastic characteristics generally have at least two phases. These phases are a martensite phase, which has a relatively low tensile strength and which is stable at relatively low temperatures, and an austenite phase, which has a relatively high tensile strength and which is stable at temperatures higher than the martensite phase.
Shape memory characteristics are imparted to the alloy by heating the metal at a temperature above which the transformation from the martensite phase to the austenite phase is complete, i.e. a temperature above which the austenite phase is stable (the Af temperature). The shape of the metal during this heat treatment is the shape xe2x80x9crememberedxe2x80x9d. The heat treated metal is cooled to a temperature at which the martensite phase is stable, causing the austenite phase to transform to the martensite phase. The metal in the martensite phase is then plastically deformed, e.g. to facilitate the entry thereof into a patient""s body. Subsequent heating of the deformed martensite phase to a temperature above the martensite to austenite transformation temperature causes the deformed martensite phase to transform to the austenite phase and during this phase transformation the metal reverts back to its original shape if unrestrained. If restrained, the metal will remain martensitic until the restraint is removed.
Methods of using the shape memory characteristics of these alloys in medical devices intended to be placed within a patient""s body present operational difficulties. For example, with shape memory alloys having a stable martensite temperature below body temperature, it is frequently difficult to maintain the temperature of the medical device containing such an alloy sufficiently below body temperature to prevent the transformation of the martensite phase to the austenite phase when the device was being inserted into a patient""s body. With intravascular devices formed of shape memory alloys having martensite-to-austenite transformation temperatures well above body temperature, the devices can be introduced into a patient""s body with little or no problem, but they must be heated to the martensite-to-austenite transformation temperature which is frequently high enough to cause tissue damage and very high levels of pain.
When stress is applied to a specimen of a metal such as Nitinol exhibiting superelastic characteristics at a temperature above which the austenite is stable (i.e. the temperature at which the transformation of martensite phase to the austenite phase is complete), the specimen deforms elastically until it reaches a particular stress level where the alloy then undergoes a stress-induced phase transformation from the austenite phase to the martensite phase. As the phase transformation proceeds, the alloy undergoes significant increases in strain but with little or no corresponding increases in stress. The strain increases while the stress remains essentially constant until the transformation of the austenite phase to the martensite phase is complete. Thereafter, further increase in stress are necessary to cause further deformation. The martensitic metal first deforms elastically upon the application of additional stress and then plastically with permanent residual deformation.
If the load on the specimen is removed before any permanent deformation has occurred, the martensitic specimen will elastically recover and transform back to the austenite phase. The reduction in stress first causes a decrease in strain. As stress reduction reaches the level at which the martensite phase transforms back into the austenite phase, the stress level in the specimen will remain essentially constant (but substantially less than the constant stress level at which the austenite transforms to the martensite) until the transformation back to the austenite phase is complete, i.e. there is significant recovery in strain with only negligible corresponding stress reduction. After the transformation back to austenite is complete, further stress reduction results in elastic strain reduction. This ability to incur significant strain at relatively constant stress upon the application of a load and to recover from the deformation upon the removal of the load is commonly referred to as superelasticity or pseudoelasticity. It is this property of the material which makes it useful in manufacturing self-expanding surgical fasteners. The prior art makes reference to the use of metal alloys having superelastic characteristics in medical devices which are intended to be inserted or otherwise used within a patient""s body. See for example, U.S. Pat. No. 4,665,906 (Jervis) and U.S. Pat. No. 4,925,445 (Sakamoto et al.).
A superelastic fastener made of a shape memory alloy is disclosed in U.S. Pat. No. 5,217,486 by Rice et al. The Rice et al. patent discloses a suture anchor that is inserted into a hole drilled into bone and lodges therein. A barb like portion of the anchor is formed from the shape memory alloy and bends to permit ingress of the fastener into the hole and digs in to prevent retraction therefrom. The suture anchor is described as being formed from a number of parts and uses suture to attach tendons or prosthetics to bone. Rice et al. does not disclose the use of this fastener onto tissue.
A superelastic fastener made of a shape memory alloy is also disclosed in a U.S. Pat. No. 6,133,611 by Allen et al. Allen teaches a surgical fastener that is stored within the application instrument as a straight wire which, when placed into tissue, automatically assumes a shape (helical or corkscrew) that compress tissue. However, the Allen et al device can only feed one fastener at a time. Additionally, no mention of its use is made in the repair of a hernia
What is needed is a simple, one-piece fastener that can fit into a 3 mm or smaller shaft and reliably attach a prosthetic or mesh patch onto tissue. A plurality of these fasteners would be stored within the shaft and body of the instrument in a serial fashion and would be deformable to fit within the shaft and expandable to attach a prosthetic onto tissue. Additionally, it would be desirable to have a fastener that can be placed and retained within Coopers Ligament.
A surgical fastener for attaching a prosthesis to body tissue formed from a generally planar continuous body member. The body has a proximal end, a distal end and a longitudinal axis therebetween. The body is preferably made from a superelastic nickel titanium alloy. The device further includes at least one, but preferably two, resilient barbs extending proximally and axially away from the distal end, preferably in different directions. The device further includes and at least one, but preferably two, resilient legs extending proximally and axially away from the proximal end, preferably in different directions. The barbs and the legs are also preferably made from a superelastic nickel titanium alloy.